Starting Out with Programming Logic and Design PDF

Starting out with Programming Logic and Design Sixth Edition Chapter 5 Modules Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved Le...

Starting out with Programming Logic and Design Sixth Edition Chapter 5 Modules Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved Learning Objectives 5.1 Introduction 5.2 Defining and Calling a Module 5.3 Local Variables 5.4 Passing Arguments to Modules 5.5 Global Variables and Global Constants 5.6 Focus on Languages: Java, Python, and C++ Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.1 Introduction (1 of 2) A module is a group of statements that exists for the purpose of performing a specific task within a program. Most programs are large enough to be broken down into several subtasks. Divide and conquer: It’s easier to tackle smaller tasks individually. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.1 Introduction (2 of 2) Benefits of using modules – Simpler code ▪ Small modules easier to read than one large one – Code reuse ▪ Can call modules many times – Better testing ▪ Test separate and isolate then fix errors – Faster development ▪ Reuse common tasks – Easier facilitation of teamwork ▪ Share the workload – Easier Maintenance ▪ Smaller, simpler code is easier to maintain Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (1 of 7) The code for a module is known as a module definition. Module showMessage() Display "Hello world." End Module To execute the module, you write a statement that calls it. Call showMessage() Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (2 of 7) A module’s name should be descriptive enough so that anyone reading the code can guess what the module does. No spaces in a module name. No punctuation. Cannot begin with a number. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (3 of 7) Definition contains two parts – A header ▪ The starting point of the module – A body ▪ The statements within a module Module name() Statement Statement Etc… End Module Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (4 of 7) A call must be made to the module in order for the statements in the body to execute. Figure 5-2 The main module Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (5 of 7) When flowcharting a program with modules, each module is drawn separately. Figure 5-6 Flowchart for Program 5-1 Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (6 of 7) A top-down design is used to break down an algorithm into modules by the following steps: – The overall task is broken down into a series of subtasks. – Each of the subtasks is repeatedly examined to determine if it can be further broken down. – Each subtask is coded. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.2 Defining and Calling a Module (7 of 7) A hierarchy chart gives a visual representation of the relationship between modules. The details of the program are excluded. Figure 5-9 A hierarchy chart Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.3 Local Variables (1 of 3) A local variable is declared inside a module and cannot be accessed by statements that are outside the module. A variable’s scope is the part of the program in which the variable can be accessed. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.3 Local Variables (2 of 3) Duplicate Variable Names: Variables within the same scope must have different names. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.3 Local Variables (3 of 3) Duplicate Variable Names: Variables in different scopes can have the same name. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.4 Passing Arguments to Modules (1 of 3) Sometimes, one or more pieces of data need to be sent to a module. An argument is any piece of data that is passed into a module when the module is called. A parameter is a variable that receives an argument that is passed into a module. The argument and the receiving parameter variable must be of the same data type. Multiple arguments can be passed sequentially into a parameter list. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.4 Passing Arguments to Modules (2 of 3) Figure 5-17 Two arguments passed into two parameters Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.4 Passing Arguments to Modules (3 of 3) Pass by Value vs. Pass by Reference Pass by Value means that only a copy of the argument’s value is passed into the module. – One-directional communication: Calling module can only communicate with the called module. Pass by Reference means that the argument is passed into a reference variable. – Two-way communication: Calling module can communicate with called module; and called module can modify the value of the argument. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.5 Global Variables & Global Constants (1 of 2) A global variable is accessible to all modules. Should be avoided because: – They make debugging difficult – Making the module dependent on global variables makes it hard to reuse module in other programs – They make a program hard to understand Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.5 Global Variables & Global Constants (2 of 2) A global constant is a named constant that is available to every module in the program. Since a program cannot modify the value of a constant, these are safer than global variables. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (1 of 9) In Java, modules are called methods. To create a method in Java, you must write its definition, which consists of : – A header that specifies the method’s name – A method body which is a collection of statements that are performed when the method is executed public static void showMessage() Header { System.out.println("Hello world"); Body } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (2 of 9) When a method is called, the program branches to that method and executes the statements in its body. showMessage(); Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (3 of 9) Local Variables – Variables that are declared inside a method are local variables. – Statements outside a method cannot access that method’s local variables. public static void myMethod() { int value = 5; System.out.println(value); } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (4 of 9) Passing Arguments to Methods – To pass an argument into a method, you must declare a parameter variable in that method's header – The parameter variable will receive the argument that is passed when the method is called public static void displayValue(int num) { System.out.println("The value is " + num); } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (5 of 9) Passing Arguments to Methods – To pass an argument into a method, you must declare a parameter variable in that method's header – The parameter variable will receive the argument that is passed when the method is called public static void displayValue(int num) { System.out.println("The value is " + num); } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (6 of 9) Passing Arguments to Methods displayValue(5); public static void displayValue(int num) { System.out.println("The value is " + num); } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (7 of 9) Passing Multiple Arguments showSum(10, 20); public static void showSum(int num1, int num2) { int result; result = num1 + num2; System.out.println(result); } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (8 of 9) Arguments are Passed By Value – In Java, only a copy of an argument’s value is passed into a parameter variable. – If a parameter variable is changed inside a method, it has no effect on the original argument. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Java (9 of 9) public class FieldTest Global Constants { – In Java, variables and constants public static final int VALUE = 10; cannot be declared outside of a public static void main(String[] args) class { // Statements here have access to – If you declare a variable or // the VALUE constant. constant inside a class, but outside } of all the class's methods, that public static void method2() variable or constant is known as a { class field, and will be available to // Statements here have access to // the VALUE constant. all the methods within the class. } public static void method3() { // Statements here have access to // the VALUE constant. } } Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (1 of 10) In Python we use functions to modularize code To create a function in Python, you must write its definition, which consists of : – A header that specifies the function's name – A function body which is a collection of statements that are performed when the function is executed def message(): Header print('I am Arthur,') Body print('King of the Britons.') Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (2 of 10) When a function is called, the program branches to that function and executes the statements in its body. def message(): print('I am Arthur,') print('King of the Britons.') message() Program Output I am Arthur, King of the Britons. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (3 of 10) Indentation: – In Python, each line in a block must be indented. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (4 of 10) Local Variables – Variables that are declared inside a function are local variables. – Statements outside a function cannot access that function's local variables. def myFunction(): value = 5 print(value) Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (5 of 10) Passing Arguments to Functions – To pass an argument into a function, you must declare a parameter variable in that function's header – The parameter variable will receive the argument that is passed when the function is called def double_number(value): result = value * 2 print(result) Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (6 of 10) Passing Arguments to Functions double_number(5) def double_number(value): result = value * 2 print(result) Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (7 of 10) Passing Multiple Arguments show_sum(10, 20); show_sum(num1, num2): result = num1 + num2 print(result) Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (8 of 10) Arguments are Passed By Value – In Python, only a copy of an argument’s value is passed into a parameter variable. – If a parameter variable is changed inside a function, it has no effect on the original argument. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (9 of 10) Global Variables # Create a global variable. – In Python, when a variable is my_value = 10 created by an assignment statement that is written outside all # The show_value function prints the functions in a program file, the # the value of the global variable. variable is global def show_value(): print(my_value) – A global variable can be accessed by any statement in the program # Call the show_value function. file, including the statements in any show_value() function Program Output 10 Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: Python (8 of 10) Global Constants – Python does not allow you to create true global constants – However, you can simulate them with global variables – If you do not declare a global variable with the global key word inside a function, then you cannot change the variable's assignment. Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: C++ Copyright © 2022, 2016, 2013, 2010 Pearson Education, Inc. All Rights Reserved 5.6 Focus on Languages: C++ (1 of 8) In C++ we use functions to modularize code To create a function in C++, you must write its definition, which consists of : – A header that specifies the function's name – A function body which is a collection of statements that are performed when the function is executed void showMessage() Header { cout